China's Tianwen-1 spacecraft, which has been orbiting Mars for almost five years, recently looked away from the planet to photograph a rare comet from outside our solar system. The spacecraft successfully captured images of the comet, known as 3I/ATLAS, as it passed through space. This was a difficult task because the comet was moving very fast.
The ATLAS telescope first discovered the comet in July 2025. It is only the third comet from outside our solar system ever found. Scientists believe 3I/ATLAS is very old, possibly billions of years old. This makes it much older than the other two interstellar comets discovered before.
Taking the pictures was technically challenging. The camera on Tianwen-1 was designed to photograph Mars, not faint objects in deep space. The comet appeared much, much dimmer than Mars. The mission team spent weeks preparing and running computer simulations to make sure the equipment could capture the images. They succeeded in taking 57 photos between September 30 and October 3, 2025. The closest the spacecraft got to the comet was about 30 million kilometers.
The photos showed the comet's center, a glowing cloud around it called a coma, and a tail. The comet is very active, losing about 1,000 kilograms of dust every second. Scientists were able to study the dust grains more accurately because Tianwen-1 was viewing the comet from a different angle than Earth-based telescopes. Data from the James Webb Space Telescope also helped scientists understand the comet's chemical makeup, which was unusual. This mission is important because it is the first time China has used a planetary exploration spacecraft for deep space observation, and the experience will help with future missions.